An MSP430-based system interfaces 4 external devices (ED0, ED1, ED2, ED3), each capable of generating an

interrupt request. The external devices place a request by setting the request line (a transition from a logic one to

a logic zero). The request lines are connected on port 1 pins P1.7, P1.6, P1.5, and P1.4, respectively. A request

line is kept active as long as the interrupt request is pending, until the request is serviced. Answer the following

questions.

If multiple requests occur at the same time, ED0 should have the lowest priority and ED3 the

highest priority. Once in the service routine multiple requests should be serviced if pending. Outline the main

steps taken in the interrupt service routine for port 1.